docs: Add a "Reset and Boot Sequence" reference page.

Previously individual ports documented these aspects to varying degrees,
but most of the information is common to all ports.

In particular, this adds a canonical explanation of `boot.py` and
`main.py`.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

2 files changed, 5 insertions, 38 deletions

diff --git a/docs/esp8266/general.rst b/docs/esp8266/general.rst
index be0437e75..d7211aa5a 100644
--- a/docs/esp8266/general.rst
+++ b/docs/esp8266/general.rst
@@ -74,40 +74,7 @@ as possible after use.
 Boot process
 ------------
 
-On boot, MicroPython EPS8266 port executes ``_boot.py`` script from internal
-frozen modules. It mounts filesystem in FlashROM, or if it's not available,
-performs first-time setup of the module and creates the filesystem. This
-part of the boot process is considered fixed, and not available for customization
-for end users (even if you build from source, please refrain from changes to
-it; customization of early boot process is available only to advanced users
-and developers, who can diagnose themselves any issues arising from
-modifying the standard process).
-
-Once the filesystem is mounted, ``boot.py`` is executed from it. The standard
-version of this file is created during first-time module set up and has
-commands to start a WebREPL daemon (disabled by default, configurable
-with ``webrepl_setup`` module), etc. This
-file is customizable by end users (for example, you may want to set some
-parameters or add other services which should be run on
-a module start-up). But keep in mind that incorrect modifications to boot.py
-may still lead to boot loops or lock ups, requiring to reflash a module
-from scratch. (In particular, it's recommended that you use either
-``webrepl_setup`` module or manual editing to configure WebREPL, but not
-both).
-
-As a final step of boot procedure, ``main.py`` is executed from filesystem,
-if exists. This file is a hook to start up a user application each time
-on boot (instead of going to REPL). For small test applications, you may
-name them directly as ``main.py``, and upload to module, but instead it's
-recommended to keep your application(s) in separate files, and have just
-the following in ``main.py``::
-
-    import my_app
-    my_app.main()
-
-This will allow to keep the structure of your application clear, as well as
-allow to install multiple applications on a board, and switch among them.
-
+See :doc:`/reference/reset_boot`.
 
 Known Issues
 ------------
diff --git a/docs/esp8266/quickref.rst b/docs/esp8266/quickref.rst
index 6f02da95d..635f1f834 100644
--- a/docs/esp8266/quickref.rst
+++ b/docs/esp8266/quickref.rst
@@ -163,10 +163,10 @@ sys.stdin.read() if it's needed to read characters from the UART(0)
 while it's also used for the REPL (or detach, read, then reattach).
 When detached the UART(0) can be used for other purposes.
 
-If there are no objects in any of the dupterm slots when the REPL is
-started (on hard or soft reset) then UART(0) is automatically attached.
-Without this, the only way to recover a board without a REPL would be to
-completely erase and reflash (which would install the default boot.py which
+If there are no objects in any of the dupterm slots when the REPL is started (on
+:doc:`hard or soft reset </reference/reset_boot>`) then UART(0) is automatically
+attached. Without this, the only way to recover a board without a REPL would be
+to completely erase and reflash (which would install the default boot.py which
 attaches the REPL).
 
 To detach the REPL from UART0, use::